This invention relates to the treatment of distillation residues from the preparation of toluene diisocyanate. More particularly the invention relates to such treatment to form products useful in the production of rigid foams.
It is known to prepare toluene diisocyanates by the phosgenation of toluene diamine. Typical processes for the phosgenation of amines may be found in U.S. Pat. Nos. 2,680,127; 2,822,373 and 3,781,320. In the phosgenation of toluene amines to form toluene diisocyanates, the product diisocyanate is generally distilled from the reaction mixture in which it is prepared. At the conclusion of the distillation, the reaction mixture normally contains a quantity of high boiling residue. Such residue generally comprises polymeric materials such as alpha, omega-isocyanatobiurets, polycarbodiimides, diisocyanato-carbodiimides, polyuretidinediones, isocyanurates and various other isocyanate adducts. Since this residue is seldom commercially useful, it it usually disposed of.
A number of processes for use of distillation residues have been developed, primarily for methylene diphenylisocyanate. Some of the processes involve reduction of acidity levels. There are many procedures known for treating organic isocyanates to reduce acidity levels. For example, U.S. Pat. No. 3,264,336 discloses a fractional distillation. U.S. Pat. No. 3,516,950 discloses a volatilization of hydrogen chloride. Other methods have been described that include treatment of organic isocyanates with certain metals, e.g., iron, copper, zinc, aluminum, nickel, cobalt and the like, organic complexes of such metals and halides salts of such metals. Such treatments generally involve separation of a reaction product from the isocyanate residue by distillation or other procedure employing heat. See U.S. Pat. Nos. 3,155,699; 3,264,336; 3,373,182 and 3,458,558. The heat is often sufficient to increase viscosity of the isocyanate residue.
A method of chloride hydrolysis for reduction of hydrolyzable chloride in isocyanates is described in U.S. Pat. No. 3,179,680. Acidity can be reduced concurrently with chloride removal by volatilization of hydrogen chloride present. (See U.S. Pat. No. 3,516,950). Epoxide compounds have been employed in reaction processes as acid acceptors (see for example U.S. Pat. No. 3,448,046). Certain epoxide compounds have also been suggested for use in reducing acidity and hydrolyzable chlorides in certain isocyanate compounds, as disclosed in U.S. Pat. Nos. 3,793,362; 3,925,437 and East German Patent 238,988 to Baum et al. The products of processes taught in the first two references are specific to polymethylene polyphenylisocyanates. The products of processes taught in Baum reference are often unsatisfactory for producing useful polyurethane foams.
Certain toluene diisocyanate residues have been mixed with certain amounts of methylene bis(phenylisocyanate) according to processes described in U.S. Pat. Nos. 3,634,361 and 3,455,836. Several uses of such mixtures are suggested including making certain polyurethanes. These too, have limited utility. Distillation residues of toluene diisocyanate have not generally proven useful in forming foams having good insulative qualities.
Rigid foams are useful in a variety of applications including insulative foams, flotation devices, furniture, decorative materials, high density structural foams and the like. Insulative rigid foams are used, for instance, to insulate vessels; pipelines; ice chests; appliances such as refrigerators; buildings and the like. Laminates of such insulative foams are used in roofing, sheathing and the like.
For use in insulation, a foam is advantageously a poor thermal conductor. Thermal conduction is measured by the K factor as described in ASTM C 177-85 and C-518-76. The lower the value of its K factor, the better insulator a material is.
It is, therefore, desirable to treat toluene diisocyanate distillation residues such that they are useful in making products such as rigid foams. Desirably, such foams have lower K factors than other, similar foams.